ci: add directive in dune to generate opam file

dune-project

@@ -1,5 +1,6 @@
 (lang dune 3.7)
 (using menhir 2.1)
+(generate_opam_files true)
 
 (package
  (name ollisp))

ollisp.opam

@@ -0,0 +1,20 @@
+# This file is generated by dune, edit dune-project instead
+opam-version: "2.0"
+depends: [
+  "dune" {>= "3.7"}
+  "odoc" {with-doc}
+]
+build: [
+  ["dune" "subst"] {dev}
+  [
+    "dune"
+    "build"
+    "-p"
+    name
+    "-j"
+    jobs
+    "@install"
+    "@runtest" {with-test}
+    "@doc" {with-doc}
+  ]
+]